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Best filament motion sensor? Design or buy?

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mushroom:
I know, 6 months...

The answer :



https://github.com/yet-another-average-joe/The_Smart_Spool_Holder

Designed this a few years ago, still using it. Saved a print yesterday.
Not for all machines, but easy to redesign if needed.
Will not detect a clogged hotend, but will never fail in other situations (it just can't) : tangles, end of spool, broken filament.
Costs nearly nothing. No sensors that never work. Mechanical problem solved with a mechanical answer = simple design (didn't find how to make this work with one switch only, keeping the design simple).
If Marlin is properly configured, the print cannot fail : M600 -> replace filament and resume.

Mechatrommer:

--- Quote from: thm_w on January 14, 2022, 10:06:13 pm ---Can Marlin measure the current from TMC2208/9 and report back? Otherwise you are building a current measurement system which seems just as complicated.
Although it may have other benefits.


--- Quote from: mazurov on January 14, 2022, 09:21:25 pm ---If you want filament motion sensor take a look at Infidel and use raw (non-averaged) signal to detect motion.  You may need to add a signal conditioning circuit to it to better see small changes.

--- End quote ---
https://github.com/drspangle/infidel-sensor
Interesting idea

--- End quote ---
i think its to read filament diameter, maybe good to detect if filament exhausted, not to detect stucked filament.


--- Quote from: Zucca on January 15, 2022, 02:05:22 am ---
--- Quote from: mazurov on January 14, 2022, 09:21:25 pm ---What is the problem you're trying to solve?

--- End quote ---
see picture Tangled spool, I want to stop/pause the printer when the spool is tangled.

--- End quote ---
thats the result of unspooling and then respooling incorrectly.

..i'm thinking of similar construction like the infidel sensor "clip" mechanism but using optical encoder (instead of magnet and hall) to detect whether filament is moving or not. and then modify marlin's code for extruder stepper motor movement based on filament movement (encoder)... its like closed loop motor. but it will take some courage to built the sensor and recode the marlin. ymmv.

Ian.M:
The problem is: when the filament has stopped moving because of a jam, the print is already compromised.  Also unless you have a Bowden feed setup, or mount the filament sensor on your direct drive printhead (undesirable because of added weight, obstruction to access for filament loading, and the extra wires needed to the printhead), the filament motion is not well correlated with extruder stepper movement, due to the printhead motion pulling on the filament above it. 

Furthermore, in non-Bowden setups, a filament jam is likely to pull hard enough on the gantry as the head carriage moves to cause the X stepper to loose steps (or Y as well in a CoreXY machine), and before extrusion fails completely, compromise the layer height by deflecting the gantry and head carriage, either or both resulting in a failed print before the lack of extrusion fails it.

To avoid this and pause the print before it fails, you need to detect the jam as it starts to occur.  It would be worth investigating a filament tension sensor, consisting of three V grooved ball bearings in the same plane with the filament running over them, two fixed on one side of the filament and one on the other side, between the first two, on a sprung lever arm that operates a microswitch.  If the filament tension becomes excessive it will attempt to straighten the filament path through the bearings, deflecting the lever against the (adjustable) spring tension, and operating the microswitch.   

You'd probably also want a filament runout sensor to detect filament breaks.

mushroom:

--- Quote from: Ian.M on Yesterday at 05:16:34 am ---...It would be worth investigating a filament tension sensor...

--- End quote ---

This is exactly what my design does. And it 100% works.
But it's not complicated/expensive enough.


--- Quote from: Ian.M on Yesterday at 05:16:34 am ---If the filament tension becomes excessive it will attempt to straighten the filament path through the bearings, deflecting the lever against the (adjustable) spring tension, and operating the microswitch.

--- End quote ---

This cannot work because the filament is not sstraight ; it has a curvature, and this curvature is not the same from the beginning to the end. And what about PETG vs TPU ?

Ian.M:
Certainly the filament isn't straight, as can be clearly seen if you lay an offcut on a flat surface, and if you wanted to *MEASURE* small tensions accurately, this would be a problem.  However you only need to detect over-tension before it jams completely, so as long as the distance between the V groove bearings is sufficiently large compared to the filament diameter, so that the force due to the stiffness of the filament is small compared to the force due to tension at the over-tension threshold, and the filament is deflected through a sufficient angle by the middle roller so that it remains in contact in spite of its curvature, when not under tension, the usual three roller method of running tension measurement is very likely to be practicable.

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